The present invention relates to a method of making a semiconductor device, and in particular to a method of forming a TiN film serving as an adhesive layer by the use of tungsten (W) or the like for filling a contact hole or the like in a semiconductor device.
When a blanket tungsten (W) film is used as a via-filler of a contact hole or the like, a reactive TiN film is often used as an adhesive layer for the tungsten film. The process flow for the formation of the blanket tungsten is shown in FIG. 4A to FIG. 4D. First, a doped or implanted layer 2 is formed at the surface of a Si substrate 1, and an interlayer insulating film 3 of for example BPSG (borophosphosilicate glass) is deposited. A contact hole 5 is then formed by optical lithography to obtain a structure shown in FIG. 4A. Reactive TiN 6 is deposited by sputtering as an adhesive layer for preventing peeling-off of a blanket tungsten film 8 used in a subsequent step. With the TiN film alone, the resistance of the contact is high, so that a pure Ti film 4 is laid (as shown in FIG. 4B), and then a reactive TiN film 6 is deposited. To make the contact Ohmic, annealing is conducted. This turns the Ti layer into a low-resistance TiSi.sub.2 layer 7 between the reactive TiN film 6 and the Si substrate 1 (as shown in FIG. 4C). Finally a blanket tungsten film 8 is deposited by CVD ( chemical vapor deposition ), and etching-back, by means of reactive ion etching for example, is conducted to leave tungsten in the contact hole as shown in FIG. 4D. Interconnection, of aluminum for example, is thereafter formed, being in contact with the blanket tungsten film 8.
The above-described method has a shortcoming in that the reactive TiN film or its underlying Ti layer being formed by sputtering has a poor step coverage, and Ti and TiN are difficult to deposit inside the contact hole. This leads to an increase in the resistance of the contact resistance and diffusion of tungsten into the Si substrate during the annealing, and an increase of the leakage current. Moreover, because of the poor step coverage, control of the thicknesses of the Ti and TiN inside the contact hole is difficult.